The safety of operation in elevator installations has to be constantly monitored, which embraces, for example, monitoring of the closing state of the doors, monitoring of travel speed and safeguarding against overloading. Such control and monitoring requires detection of values, on the basis of which an actual state is continuously compared with a target state during operation. This is usually carried out by controls and checking devices which allow time-dependent and travel-dependent detection of operating data.
In the case of elevator installations with a counterweight in which a support means is guided in accordance with a block-and-tackle principle (for example 2:1, 4:1 or 6:1 installations), the support cables or support belts on the car side as well as on the counterweight side are, for example, guided over deflecting rollers. On occasion, substantial forces, with which a high level of material loading is connected, act on these deflecting rollers. In particular, bearing damage can arise due to wear. Bearing damage of that kind can as a consequence of increased friction lead to substantial forces or torques on the bearing parts. This can, for example, have the consequence that a stationary axle body is rotated out of its fixing. This undesired rotational movement can lead to consequential damage of the suspension up to the point of total failure of the bearing with possible consequential damage of the elevator installation.
It is known from EP 0 824 495 B1 to monitor the movement states and/or rotational states of components, which are rotatable relative to one another, of a roller bearing. The monitoring is carried out by pulse transmitters or by way of other means for signal detection, which are integrated in the roller bearing. However, roller bearings of that kind are cost-intensive and complicated with regard to system integration. In particular, connection with a control of the elevator installation is required, which can be complicated in the case of roller bearings arranged at moved components.
Moreover, a load lifting device with use of the block-and-tackle principle has become known from DE 20 2009 013349 U1, which comprises a monitoring device for detection of a relative movement between the cable loop and a center roller.